it fails at checking prerequisites and I see the following messages in the log:

---------------------------------------
INFO: Physical Memory: This is a prerequisite condition to test whether the system has at least 1GB (1048576.0KB) of total physical memory.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:1GB (1048576.0KB)
INFO: Actual Value:992.41MB (1016228.0KB)
INFO: Error Message:PRVF-7530 : Sufficient physical memory is not available on node "dev01-cs-ord1" [Required physical memory = 1GB (1048576.0KB)]
INFO: Cause: Amount of physical memory (RAM) found does not meet minimum memory requirements.
INFO: Action: Add physical memory (RAM) to the node specified.
INFO: *********************************************
INFO: Package: libaio-0.3.105: This is a prerequisite condition to test whether the package "libaio-0.3.105" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:libaio-0.3.105 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "libaio-0.3.105 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: glibc-2.3.4-2.41: This is a prerequisite condition to test whether the package "glibc-2.3.4-2.41" is available on the system.
INFO: Severity:CRITICAL
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:glibc-2.3.4-2.41 (i686)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "glibc-2.3.4-2.41 (i686)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: compat-libstdc++-33-3.2.3: This is a prerequisite condition to test whether the package "compat-libstdc++-33-3.2.3" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:compat-libstdc++-33-3.2.3 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "compat-libstdc++-33-3.2.3 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: libgcc-3.4.6: This is a prerequisite condition to test whether the package "libgcc-3.4.6" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:libgcc-3.4.6 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "libgcc-3.4.6 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: unixODBC-2.2.11: This is a prerequisite condition to test whether the package "unixODBC-2.2.11" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:unixODBC-2.2.11 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "unixODBC-2.2.11 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: pdksh-5.2.14: This is a prerequisite condition to test whether the package "pdksh-5.2.14" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:pdksh-5.2.14
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "pdksh-5.2.14" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
--------------------------------------------

Interesting thing, that that most of these packages are already installed, but the version is newer than what installer is looking for.

My questions:

1. Do I really need to install the exact version of each package or is there a way to instruct the installer just use the latest?
2. Isn't "yum install oracle-rdbms-server-11gR2-preinstall.x86_64" supposed to install all required packages for me, so I don't deal with these kind of errors?
3. Can I ignore the errors with "Severity: Ignorable"?

it fails at checking prerequisites and I see the following messages in the log:

---------------------------------------
INFO: Physical Memory: This is a prerequisite condition to test whether the system has at least 1GB (1048576.0KB) of total physical memory.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:1GB (1048576.0KB)
INFO: Actual Value:992.41MB (1016228.0KB)
INFO: Error Message:PRVF-7530 : Sufficient physical memory is not available on node "dev01-cs-ord1" [Required physical memory = 1GB (1048576.0KB)]
INFO: Cause: Amount of physical memory (RAM) found does not meet minimum memory requirements.
INFO: Action: Add physical memory (RAM) to the node specified.
INFO: *********************************************
INFO: Package: libaio-0.3.105: This is a prerequisite condition to test whether the package "libaio-0.3.105" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:libaio-0.3.105 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "libaio-0.3.105 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: glibc-2.3.4-2.41: This is a prerequisite condition to test whether the package "glibc-2.3.4-2.41" is available on the system.
INFO: Severity:CRITICAL
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:glibc-2.3.4-2.41 (i686)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "glibc-2.3.4-2.41 (i686)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: compat-libstdc++-33-3.2.3: This is a prerequisite condition to test whether the package "compat-libstdc++-33-3.2.3" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:compat-libstdc++-33-3.2.3 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "compat-libstdc++-33-3.2.3 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: libgcc-3.4.6: This is a prerequisite condition to test whether the package "libgcc-3.4.6" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:libgcc-3.4.6 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "libgcc-3.4.6 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: unixODBC-2.2.11: This is a prerequisite condition to test whether the package "unixODBC-2.2.11" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:unixODBC-2.2.11 (i386)
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "unixODBC-2.2.11 (i386)" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
INFO: *********************************************
INFO: Package: pdksh-5.2.14: This is a prerequisite condition to test whether the package "pdksh-5.2.14" is available on the system.
INFO: Severity:IGNORABLE
INFO: OverallStatus:VERIFICATION_FAILED
INFO: -----------------------------------------------
INFO: Verification Result for Node:dev01-cs-ord1
INFO: Expected Value:pdksh-5.2.14
INFO: Actual Value:missing
INFO: Error Message:PRVF-7532 : Package "pdksh-5.2.14" is missing on node "dev01-cs-ord1"
INFO: Cause: A required package is either not installed or, if the package is a kernel module, is not loaded on the specified node.
INFO: Action: Ensure that the required package is installed and available.
--------------------------------------------

Interesting thing, that that most of these packages are already installed, but the version is newer than what installer is looking for.

My questions:

1. Do I really need to install the exact version of each package or is there a way to instruct the installer just use the latest?
2. Isn't "yum install oracle-rdbms-server-11gR2-preinstall.x86_64" supposed to install all required packages for me, so I don't deal with these kind of errors?
3. Can I ignore the errors with "Severity: Ignorable"?

That would be strange. I thought CentOS was closely following RedHat releases and CentOS 6 would be pretty similar to RedHat 6. Also, I see there are instructions on the internet on how to install Oracle 11g on CentOS 6. Though all of them talk about installation in GUI environment and not at command line, but that shouldn't affect the prerequisites check in my opinion.

colddata wrote:
That would be strange. I thought CentOS was closely following RedHat releases and CentOS 6 would be pretty similar to RedHat 6. Also, I see there are instructions on the internet on how to install Oracle 11g on CentOS 6. Though all of them talk about installation in GUI environment and not at command line, but that shouldn't affect the prerequisites check in my opinion.

colddata wrote:
That would be strange. I thought CentOS was closely following RedHat releases and CentOS 6 would be pretty similar to RedHat 6.

Regardless, CentOS is not a supported distro.

Also, I see there are instructions on the internet on how to install Oracle 11g on CentOS 6. Though all of them talk about installation in GUI environment and not at command line, but that shouldn't affect the prerequisites check in my opinion.

There is a lot of stuff on the internet ;-) some legit, some not so legit. I am pretty confident none of the links you refer to are on an official Oracle website.

Currently, 11.2.0.3 is the only certified version on RH6 - http://docs.oracle.com/cd/E11882_01/relnotes.112/e23558/toc.htm#CHDFHIEA - and 11.2.0.3 is only available on My Oracle Support for customers with a paid support contract. If you are installing a version lower than 11.2.0.3, you will need to use Linux 5.x

Yes, we need to match the client's environment who's on RedHat 5. Based on my research, I found that CentOs was the closest to RH and it was free. I guess my only option is to go with RedHat 5 and paying monthly fees. Bummer.